Description The Portuguese Man o' War (Physalia physalis), also known as the Portuguese man-of-war, man-of-war, or bluebottle, is a jelly-like marine invertebrate of the family Physaliidae. The name "man-of-war" is taken from the man-of-war, a 16th century English armed sailing ship which was based on an earlier Portuguese vessel.

Despite its outward appearance, the Man o' War is not a true jellyfish but a siphonophore, which differ from jellyfish in that they are not actually a single creature, but a colonial organism made up of many minute individuals called zooids. Each of these zooids is highly-specialized and, although structurally similar to other solitary animals, are attached to each other and physiologically integrated to the extent that they are incapable of independent survival.

The Man o' War is found in warm water seas floating on the surface of open ocean, its air bladder keeping it afloat and acting as a sail while the rest of the organism hangs below the surface. It has no means of self-propulsion and is entirely dependent on winds, currents, and tides. It is most common in the tropical and subtropical regions of the Pacific and Indian oceans, but can drift outside of this range on warm currents such as the Atlantic Gulf Stream.

Warning Highly toxic. The tentacles contain one of the most powerful poisons known in marine animals and can inflict severe burns and blisters even when the animal is dead on the beach.